jrb551,
One of the first things that I would want to verify is the actual oil being used. Is it actually the proper oil? The actual oil used may be too viscous either by deliberate choice or by poor oil quality control.
A problem that I have encountered several times is the substitution of more viscous lube oil in "hot" applications. The innocent concern was that the oil would not have adequate viscosity to protect lubricated surfaces, so thicker oil was deliberately used. In reality, the more viscous oil produced inferior lubrication and even higher temperatures due to diminished flow and diminished oil cooler performance. Another problem with more viscous lube oil is poor spray patterns, poor splash distribution, and dimished flows for cooling.
I can readily imagine a situation such as yours where "low oil pressure" was noticed, and heavier oil was substituted to "correct" that "problem." If so, it is likely that the indicated oil pressure was then restored by effectively restricting the flow where it was needed while a significant portion of the oil pump's delivery was by-passed through the pressure relief valve.